Semiconductor devices such as individual integrated circuit (IC) dies are packaged by attaching the individual IC dies to a substrate, and then encapsulating the individual IC dies and portions of the substrate in a mold compound.
The performance of some components on semiconductor devices degrade when the components come into contact with mold compound. For example, the electrical properties of some components on semiconductor devices can be changed by stress due to the mold compound to the extent that the semiconductor device can fail.
Mold compound can be a liquid at room temperature or a solid at room temperature. If a solid at room temperature, the mold compound can be heated to a molten state prior to molding. The mold compound is injected into a mold containing the substrate and a semiconductor device die. After the mold compound cools, the packaged semiconductor device is removed from the mold. During curing and cooling the mold compound shrinks, and as the mold compound shrinks it applies compressive stress to the semiconductor device. The semiconductor device may contain a component with electrical properties that are degraded by compressive stress. Example components on semiconductor devices that are subject to changing electrical properties due to mold compound stress include: a bipolar junction transistor (BJT); an analog transistor; a sensor; and a bulk acoustic wave (BAW) device.
Mold compound used in semiconductor packaging can change electrical properties sufficiently to degrade the performance of the semiconductor device to fail.